1. Field of the Invention
The invention relates in general to a viewing-angle adjustable liquid crystal display and method for adjusting viewing angle of same, and more particularly to a viewing-angle adjustable liquid crystal display, which can provide the required viewing-angle mode for the user by electrical signal switching, and method for adjusting viewing angle of same.
2. Description of the Related Art
As technology makes progress, consumers have more opportunities of using mobile devices equipped with liquid crystal displays, such as mobile phones or notebook computers, in public regions. As using the mobile device in a public region, the consumer often need the mobile device to have a viewing-angle adjustable display so as to keep the displayed images secret. At present, there are three kinds of well-known liquid crystal display viewing-angle control methods.
FIG. 1 is a schematic diagram of using shutter structure to adjust the liquid crystal display viewing-angle. Referring to FIG. 1, the shutter structure 110 is disposed in front of the liquid crystal display 100 and has the shutters arranged in parallel. By adjusting the height h of the shutter structure 110 and the distance I between two adjacent shutters, the light L emitted by the display 100 can be restricted to reach eyes of the observers at some specific viewing-angles. Therefore, only within the viewing angle region spreading the angle θ as shown in the figure, the light L can pass the absorbing materials 110 and the observer at these viewing angles can thus see the images on the display 100 while the light L emitted beyond the viewing-angle region of the angle θ, will be absorbed by the absorbing materials 110.
However, the viewing-angle control method has the following disadvantages. The shutter structure 110, as used, should be additionally configured at the exterior of the display, thereby causing the inconvenience in usage. Since a part of the light L is absorbed by the shutter structure 110, the display luminance will be lowered down at least a half. Moreover, the shutter structure 110 can only provide a left side viewing-angle mode or a right side viewing-angle mode, which will not meet the user's requirement of various view-angle modes; for example, only the users at front view and the left-side view can observe the displayed images.
FIG. 2A and FIG. 2B are schematic diagrams of using a light scattering device to adjust the liquid crystal display viewing-angle. The light scattering device 210, such as a polymer dispersed liquid crystal (PDLC) layer, in which light scattering features can be adjusted, is disposed between the parallel backlight (Lb) device (not shown in the figure) and the liquid crystal cell 200. By adjusting the voltage applied to the light scattering device 210, the narrow viewing-angle mode and the wide viewing-angle mode can be provided. As shown in FIG. 2A, under the narrow viewing-angle mode, the light scattering device 210 is in the power on state, and appears transparent so that the backlight Lb is maintained parallel after passing the light scattering device 210 to reach the liquid crystal cell 200. Therefore, only the front view observer can see the displayed images. As shown in FIG. 2B, under the wide viewing-angle mode, the light scattering device 210 is in the power off state, the backlight Lb is scattered to form the scattering light Ls and enter the liquid crystal layer 200 so that the observers at every viewing angle can see the displayed images.
However, this viewing angle control method has the following disadvantages. When the light scattering device 210 is switched to the power on state, a part of the backlight Lb will be reflected as passing the light scattering device 210, thereby reducing the luminance of the liquid crystal panel 200. In addition, as the above-mentioned example, this viewing angle control method can only provide the narrow viewing angle mode for front view observers, but not for the user at any other viewing angle, thereby reducing the available options in viewing-angle adjusting.
FIG. 3A and FIG. 3B are schematic diagrams of controlling display viewing-angles by using an extra alignment layer. By adjusting the rubbing direction of the alignment layer additionally disposed on the liquid crystal display, a wide viewing-angle mode and a narrow viewing-angle mode can be provided. As shown in FIG. 3A, under the narrow viewing-angle mode, the front view observer can see the displayed image 300 while the side-view observer cannot distinguish the displayed image 300 because a specific picture 310 having alternate bright and dark squares covers the image 300 as shown in FIG. 3B. By doing so, the viewing-angle adjusting purpose can be achieved.
However, as shown in the above-mentioned three examples, the present viewing-angle adjustable liquid crystal display structures have the disadvantage of the luminance and bright contrast deviation as the viewing angle modes are switched. Also they cannot provide the narrow viewing-angle mode for users at other viewing-angles except the front view ones. Therefore, such viewing-angle adjusting methods are not satisfied.